This invention relates generally to fuel injectors of the type that are used to inject liquid fuel into the induction system of an internal combustion engine and having an atomizer that fits over the tip end of the injector to promote the atomization of the liquid fuel ejected by the fuel injector, and particularly to metering and directing the air required for an air assist fuel injector.
Air assist atomization of the liquid fuel ejected from the tip end of a fuel injector is a known technique that is used to promote better preparation of the combustible air/fuel mixture that is introduced into the combustion chambers of an internal combustion engine. A better mixture preparation promotes both a cleaner and a more efficient combustion process, a desirable goal from the standpoint of both exhaust emissions and fuel economy.
Future engine emission requirements have driven the need to achieve better atomization of the fuel, breaking up the liquid fuel into small droplet size that would result in more thorough or efficient combustion. The improved atomization has been accomplished by a technique generally referred to as xe2x80x98air assistxe2x80x99, whereby when additional air at sonic velocity is aimed at the fuel, the impact of the air results in the air energy breaking up the liquid fuel droplets into droplets of a fine mist. This is then still aimed at the intake valve.
The state of the art contains a substantial number of patents relating to air assist atomization technology. The technology recognizes the benefits that can be gained by the inclusion of special assist air passages that direct the assist air into interaction with the ejected liquid fuel. Certain air assist fuel injection systems use pressurized air, from either a pump or some other source of pressurization, as the assist air. Other systems rely on the pressure differential that exists between the atmosphere and the engine""s induction system during certain conditions of engine operation. It is a common technique to mount the fuel injectors in an engine manifold or fuel rail or engine head which is constructed to include assist air passages for delivering the assist air to the individual injectors.
Although several different methods of metering the air stream have been successful, one of the challenges in mass production of air assist fuel injectors remains in being able to take a production injector, and with a minimum number of design and processing changes, make it easily adaptable to an air assist application. Typically the design consists of three main parameters, which include the actual metering of the air to accomplish a known flow, a component for directing the flow, and the packaging required to contain the necessary seals to the engine.
One of the past concepts utilized a cup shaped metal air shroud, containing a through hole of limited size on the bottom of the cup. The cup was attached to the injector by welds through the side of the cup, to the outer diameter of the valve body. The air flow was metered, or restricted, by the circumference of the through hole, multiplied by the height that the through hole was away from the end of the injector. The injector shroud assembly would be flowed with air, and the height of the cup from the end of the valve body would be altered, in a calibrated manner, until the air flow desired was achieved. This concept was advantageous in that the same assembly could be utilized for a range of desired air flows, to match the range of customer demands for different air calibrations. However, the disadvantages include the requirement to have a calibrations step in the assembly/manufacturing process, which results in additional process time and cost. Furthermore, the direction of the metered air flow is perpendicular to the direction of the fluid flow, which has not been shown to be advantageous for fluid targeting geometry.
An alternative concept consisted of a metal shroud containing a metal air metering disc. The bottom portion of the cup sandwiched the disc to the end of the fuel injector, typically containing a special air metering disk at the end of the injector. The metering area was formed by the metering disc, with at least one channel allowing air passage from the outer diameter of the shroud, to the inner, exit hole of the shroud. The air shroud/metering disc assembly was attached to the valve body typically by a staking operation, deforming the shroud into the valve body. This concept had advantages in that the assembly process did not require a calibration operation, since the flow variation was kept to a minimum by the accuracy of the manufacturing process for the metering disc. Additionally, the air metering disk design was such that split stream air assist was feasible. However, the air flow in this concept is once again perpendicular to the fluid flow.
It is seen then that there exists a need for a method of air metering which allows any standard injector with a backup washer to be converted to an air assist injector, capable of air flow direction at different angles, which have targeting benefits.
This need is met by the air assist metering apparatus and method, according to the present invention. A typical injector valve body contains a retainer member; for air assist, an additional air metering device is provided. The surface of the retainer member protrudes beyond the crimp area of the valve body, and contains a flat surface which serves to seal the air metering disc. The present invention utilizes a air assist backup washer as the air metering or air directing component.
In accordance with one embodiment of the present invention, a method of air metering is provided for obtaining a desired air flow through a fuel injector. The fuel injector comprises an air assist injector valve body and an air assist backup washer, having two or more flow channels, contained within the backup washer. The fuel injector further comprises a shroud member having a flat surface, wherein the flat surface abuts up against the backup washer so the flat surface of the shroud member combined with the flow channels in the backup washer meter and/or direct the air flow.
It is an advantage of the present invention that it eliminates the need for an additional disk or insert to cooperate to provide the desired air flow. Consequently, the present invention provides the advantage of a higher quality air assist injector which is easier to manufacture.
For a full understanding of the nature and objects of the present invention, reference may be had to the following detailed description taken in conjunction with the accompanying drawings and the appended claims.